Centrifugal switch



Feb. 7, 1939. A. CUSHMAN CENTRIFUGAL SWITCH Filed Aug. 28, 1956 Patented Feb. 7, 1939 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to centrifugal switches and especially to switches of that type used for short-circuiting commutators of electric machines.

It is well known to start alternating current commutator motors with short-circuit brushes as repulsion motors, thereby obtaining favorable starting torques, and to short circuit the commutator when a certain speed has been reached whereupon the motor runs as an ordinary induction motor with short-circu'ited rotor.

Various known devices utilize radially arranged segments normally resting on a part insulated from the commutator proper, but, when rotated, moving over the commutator against the tension of a spring, under the influence of the centrifugal force which increases with increasing speed of the motor.

It is the object of the present invention to provide an improved centrifugal switch of this type which is extremely simple, and therefore of rugged and cheap construction and which is certain in operation and not liable to become inoperative due to sparking or the accumulation of I dirt. In another aspect, my invention proposes a switch element construction which permits the use of the simplest possible supporting elements as well as easy assembly and secure operation.

These and other objects will be apparent from the following description of a practical embodiment illustrating the genus of the invention. This description refers to a drawing in which:

Fig. 1 is the side elevation of a motor incorporating the invention, with the commutator side and the commutator shown partly in section;

Fig. 2 is an enlarged sectional view of a commutator with my centrifugal switch, in normal position;

Fig. 3 is a view similar to Fig. 2 with the switch in short-circuiting position; and

Figs. 4 and 5 are diagrammatic representations of the manner in which the new switch is assembled and mounted.

Referring to Fig. 1, shaft I of a motor M carries in known manner a commutator shell 2 and commutator segments 3 insulated at 5 from the shelland from each other. Shell 2 and segments 3 are beveled at 4 (Fig. 2), but without any ledge, bead or other obstruction tending to collect dust or dirt which might impair the operation of the device. Slidably mounted on shaft I is a disk II having a slightly upturned edge lip I2 (Fig. 3) and a sleeve portion I4.

Surrounding disk II are arranged contacts or centrifugal switching elements 2I, with rounded comparatively heavy contact portions 22 and hook portions 23 extending oppositely to the contact portions. Between hook and contact portions is a recessed contour 24 proportioned in relation to the commutator body in a manner making contact between these portions of the switching elements and the commutator impossible when they move relatively to each other. As shown in Figs. 2 and 3 the hook portion is confined between disk I I and shell 2, which prevent dislocation thereof. Preferably, but not necessarily, the switching elements are stamped from sheet metal and accordingly flat, as indicated in the drawing.

Fixed to shaft I for example by means of set screw 3I, is a collar 32, and a helical spring 33 is inserted between sleeve portion I4 and collar 32, tending to move disk II into the commutator shell. Spring 33 and collar 32 are so proportioned and located that complete compression of the spring stops the movement of the contact elements at a desired position thereof.

Apparatus of this type offers certain difficulties of assembly. For example, the short-circuiting switch of a motor of 3 or 4 H. P. has more than 100 switching elements which have to be assembled within the commutator. The present construction makes the assembly very easy. It is only necessary to place disk II on a horizontal table member 4| (Fig. 4) which may be provided with an annular supporting ledge as shown at 42 at the left side of Fig. 4. Switching elements 2I can now be very easily hung around the lip edge I5 of disk II. When all elements are applied, they are secured together by suitable means, for example a rubber band indicated at 43 of Fig. 4. Disk II with elements 2| can now be handled without fear of disassembly, the elastic pressing the elements towards lip I5, and against each other like the stones of a masonry arch. The disk together with the switching elements can now be inserted in upright position into commutator shell 2, as shown in Fig. 5. As soon as the reverse sides of the hook portions are within the shell, there is no danger of disassembly, the elastic or similar means can be removed, spring 33 clipped on and the assembly completed as above indicated.

The short-circuiting device according to the invention operates as follows:

In normal position when the motor is at rest, or during the slow speed starting period, the switching elements rest against the commutator shell I I, as shown in Fig. 2. As the motor gains speed, the centrifugal force tends to move contact portions 22 outwardly. Consequently they slide over the insulation 5 and begin to establish with them switching elements 2|.

contact with the commutator segments 3 which are thereupon short circuited through elements 2| and disk I I. The latter has been moved axially by the switching elements 2! swinging outwardly, spring 33 opposing the centrifugal force. When spring 33 is substantially completely compressed, sleeve 14 and disk II are stopped and It will be noted that contact portions 22 of the switching elements establish rubbing contact with the commutator segments when sliding thereupon, and that the switching elements are not stopped by an obstructing portion of the commutator where dirt will easily accumulate, but are free to rub back and forth during operation, an ultimate stop being provided through collar 32 and spring 33, as above described.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. A device of the character described comprising an armature shaft, a commutator structure mounted thereon having a commutator contact surface and a rest surface insulated therefrom, both surfaces being inclined, facing said shaft, and free of obstructing protrusions, a stop element fixed on said shaft against movement in axial direction, a disk member surrounding said shaft, a yielding element tending to separate said stop element and said disk member, and contact plates engaging said disk member with pivot hooks directed inwardly towards the shaft and having a rounded outer contact portion, said plates resting normally on said rest surface and moving under the influence of the centrifugal force axially and outwardly, thereby rubbingly contacting said contact surface and being stopped in ultimate contacting position by said stop element.

2. A device of the character described comprising an armature shaft, a commutator structure mounted thereon having a shell portion with rest surface and commutator segments with a contact surface, said surfaces being coaxial with and facing said shaft and free of obstructing protrusions, a stop element fixed on said shaft against movement in axial direction, a disk member surrounding said shaft, a yielding element tending to separate said stop element and said disk member, and contact elements having pivot hooks directed inwardly towards the shaft for engaging said disk member and rounded'outer contact portions directed substantially opposite to said hooks, said contact portions resting normally on said rest surface and moving under the influence of the centrifugal force azn'ally and outwardly, thereby rubbingly contacting said contact surface and being stopped in substantially compressed position of said yielding element.

3. A device of the character described comprising an armature shaft, a commutator structure mounted thereon having an annular contact surface, a disk member slidably mounted on said shaft, a plurality of contact elements dis posed in radial planes about said shaft, each of said elements having one end portion disposed outwardly of said disk in pivotal contact with the outer edge of the disk, each contact element also having an opposite heavier end portion which tends to swing outwardly under the action of centrifugal force thereby moving the disk axially of the shaft, and means yieldably opposing such an axial movement of the disk, the heavier end portions of the elements as they move outwardly having, a rubbing engagement with the contact surface. 7

4. A device of the character described com prising an armature shaft, a cup-like commutator structure mounted thereon having an annular contact surface at its end, a disk member slidably mounted on said shaft within said cuplike commutator structure, said disk having a beveled edgelip, a plurality of contact elements disposed in radial planes about said shaft and having end portions disposed outwardly of said disk with hook-like extremities extending inwardly toward said shaft, the contact elements having pivotal line contacts with the edge of the lip andhaving opposite heavier end portions with curved surfaces which may move into rubbing engagement with said contact surface under the action of centrifugal force, and means yieldably opposing the slidable movement of said disk on said shaft and the outward movement of said heavier end portions of the contact elements.

' ABE L. CUSHMAN. 

